Nitriding



Patented Mar. 6, 16934 NITBmING John J. Egan, Brooklyn, N. Y., assignorto Electl'o Metallurgical Company,

Virg a a corporation or West No Drawing. Application February 26, 1930,Serial No. 431,641

9 Claims. (Cl. 148-46) I My invention relates to the production ofnitride cases on ferrous materials by heating the materials in thepresence of nitriding agents, and it is the main object of my inventionto intensify or accelerate the production of such cases.

Thin, hard, wear-resistant cases on ferrous alloys are useful as wearingsurfaces for machine er-temperatures are used than when higher tem-'peratures are used. The hard, wear-resistantcases are usualy' producedby heating in an atmosphere of ammonia to about 460 C. to 580 C., thetreated alloy containing a promoting agent, such as aluminum orvanadium, which promotes the formation of the hard, wear-resistantcoating at these temperatures. By far the most extensive use of myinvention is in connection with the production of hard, wear-resistantcoatings and the invention will be described with reference thereto.

It has been found that the action of nitriding agents is intensifiedwhen a closed chain carbon compound in which nitrogen forms a part ofthe closed chain is present.

As illustrative of my invention, a specimen of ferrous alloy containingabout 95.5% iron, about 1% aluminum, and small amounts oi phosphorus,sulphur, manganese, silicon, nickel, molybdenum and carbon was placed ina closed con tainer. Ammonia was bubbled through pyridine whichwasheated to a temperature just below its boiling point to increase itsvapor pressure. The entrapped air in the container was displaced by themixture of ammonia and pyridine vapor and the container and its contentswere heated to 460 C. for 4 hours whilst a slow current of the gasmixture was passed into the container. A thin, uniform, wear-resistantcase having a hardness corresponding to about 1000 Brinell was pro-.duced on the specimen. A similar hard, wearresistant case was producedonanother specimen 0! the same alloy when heated for 16 hourswithout thepresence of pyridine vapor. By treatment with ammonia without, thepyridine, no'

appreciable hardness was produced by heating the alloy at 460 C. for 4hours.

Beneficial results may be produced by the use of other compounds of theabove described class as for example, higher molecular weightclosedtferrous materials which comprises heating the ammonia which compriseseffecting said nitriding chain carbon compounds in which at least onenitrogen radical forms a part of a closed chain. Quinoline is such acompound, and is an effective accelerator, and other compounds in whicha nitrogen atom occurs in a closed chainmay be used.

Any appreciable amount of the accelerator in conjunction with thenitriding agent is suflicient to produce acceleration. The preferredamount to be used with an alloy under given conditions may be determinedby experiment for each particular case, but the invention is of coursenot restricted to the proportion which gives the maximum effect.Considerations of cost make it desirable not to use excessive amounts ofthe accelerator substance. That is, a modicum of accelerator isgenerally suflicient. Although I have given only a few specific examplesof accelerators and only one example of a nitriding agent, it is evidentthat other substances of the classes described may beused andmodifications of the described methods may be made without departingfrom my invention. Therefore, I do not wish to be understoodas imposinglimitations on my invention except such as are imposed by the prior artand by the annexed claims.

Iclaim: 1. The method of producing nitride cases on material atnitriding temperatures below the eutectoid at about 600 C. in thepresence of ammonia and an accelerating agent consisting of a closedchain carbon compound in which one a nitrogen radical and five carbonradicals form 0 the closed chain. i

2. Method of accelerating; the production of nitride cases on ferrousmaterials by heating the materials at nitriding temperatures below thenitride eutectoid at about 600 C. in the presence oi ammonia whichcomprises efiecting -said nitriding in the presence of an acceleratingagent consisting of a closed chain carbon compound in which one nitrogenradical and iive carbon radicals form the closed chain.

3. Method of accelerating the production or nitride cases on ferrousmaterials by heating the materials at nitriding temperatures below thenitride eutectoid at about 600 C. in the presence of in. the presence ofan acceleratingagent chosen from the group comprising pyrldineandquinoline.

4. The method of producing nitridecases' on ferrous materials whichcomprises heating the 5 material at nitriding temperatures below thenitride eutectoid at about 600 C. inthe presence of ammonia and at leastone or the following: pyridine, quinoline.

5, Medium for nitriding ferrous materials comprising ammonia and amodicum of a nitriding accelerator, said accelerator consisting of aclosed chain carbon compound in which one nitrogen atom and five carbonatoms form the closed i'errous materials which comprises passing ammoniain contact with at least one liquid closed and five carbon radicals formthe closed chain, whereby a mix'tm'e oi the ammonia and the compound isiormed, and heating the material at nitriding temperatures below thenitride eutectoid atabout 600 C. in the presence of the mixture 9. Themethod of producing nitride cases on ferrous materials which comprisespassing amchain compound in which one nitrogen radical monia in contactwith at least one compound chosen from the group consisting 'of pyridineand quinoline, whereby a mixtin-e oi. the ammonia and the compoundisformed, and heating the material at nitriding temperatures below thenitride eutectoid at about 600 C. in the presence or the mixture. JOHNJ. EGAN.

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